'Race' and ethnicity have long been central concepts for social scientific inquiry. Their meaning and import have, however, changed dramatically from one era to another. Much of the work of the late nineteenth century, for example, focused on issues like competition between 'different races', on ways to improve the health of 'the race' (one's own), on the problem of miscegenation, and on the impact of immigration on the 'racial make-up' and cultural identity of national populations. Nowadays, only the last of these continues to spark serious discussion.